The present invention relates generally to an apparatus for and method of suppressing noise and, more particularly, to a suppressor for abating the noise generated in the exhaust region of a jet engine.
A serious problem associated with the use of jet engines is the generation of irritating and intolerable noise resulting from the turbulent mixing of exhaust gases from the discharge nozzle of a jet engine into the ambient atmosphere. The near and far field noise levels generated by jet aircraft can result in structural failures and increased acoustic detection signatures. In light of this, as well as the noise pollution impact, particularly in populated areas, many efforts have been made to reduce, suppress, or otherwise control the noise generated by these jet engines. Various approaches to suppress such jet noise have been proposed. Two of the more effective older methods include placing tabs or notches within the exhaust nozzle adjacent the exit end thereof. However, the specific size and number of tabs or notches required to achieve accepted noise levels is not well defined and requires objectionable structural modifications. Because of the placement of such tabs within the exhaust nozzle, they not only adversely affect engine thrust because of partial blockage of the cross sectional area of the exhaust stream, but also must be fabricated from very expensive, high temperature resistant materials.
Other prior art efforts aimed at jet engine noise suppression include corrugated or fluted exhaust nozzles, additional passages connected to the exhaust gas flow, or annular passages within the nozzle producing concentric primary exhaust and fan flows exiting the jet engine nozzle outlet. While such efforts have at least partially suppressed jet engine noises, they have not been entirely satisfactory because they only interact with one or two limited number of the mechanisms or phenomena generating the noise. Additionally, such efforts have resulted in thrust loss and an increase in base drag. Moreover, most of these nozzle configurations, as well as the tab and notch expedients noted above, are rigidly fixed and designed for only one predetermined optimum engine exhaust flow condition and cannot accommodate the different exhaust flow conditions encountered during flight.